1. Field of the Invention
This invention is in the field of fabrics and, more particularly, in the field of antistatic fabrics.
2. Description of the Prior Art
With the advent of carpeting an extremely annoying but usually not dangerous problem has plagued humans, the shock or jolt of a static electricity discharge received after walking or shuffling across a carpet and touching an electrical ground, such as a lamp, light switch, TV, or water faucet. This poblem is much more prevalent during periods of cold temperatures when the relative humidity inside a heated building is low. In an effort to eliminate this problem, many different types of solutions have been tried; for example, (1) chemical treatments (antistats) applied to the carpet-facing yarn fibers by spraying, coating, etc., (2) fine continuous metal wires (having a diameter ranging from three to ten mils) woven with the carpet facing into the backing fabric, (3) a conductive latex applied to the backing fabric, and (4) the use of special synthetic fibers that have a surface capable of sbsorbing moisture. Each of these solutions has proven unsatisfactory either because (1) it does not work at all, (2) it works for only a short period of time, (3) it works only under certain conditions, i.e., when the relative humidity is sufficiently high so that no antistatic method is really needed, or (4) it can be extremely dangerous in the case of fine electrically continuous metal wires. In fact, carpets with such continuous wires have been tested and it was found that the low electrical resistance of the continuous fine metal wire in the carpet creates the atmosphere for an electrical hazard. Under the proper conditions, a person having wet shoes or being barefoot touching a faulty lamp while standing on such a carpet can incur serious injury. In other words, such carpets under certain conditions can be extremely dangerous.
In U.S. Pat. Nos. 3,277,564 and 3,379,000, owned by the assignee hereof, Webber et al teach a new metal filament having the characteristics of a textile. Valko, in U.S. Pat. No. 3,288,175, recognized the advantages of these metal filaments and taught that if such continuous metal filaments were provided in association with continuous filament synthetic yarns and then woven into a grid structure fabric, the resulting fabric would exhibit antistatic characteristics. In order to insure an antistatic fabric, Valko teaches that there must be a continuous filament metal-to-metal contact in the yarn wherein the metal filaments comprise approximately 10% by weight of the textile fabric. Valko's continuous metal filament portion of the continuous filament yarn or the continuous metal-to-metal contact of a spun blended yarn would produce a carpet that would function similarly to the fine continuous metal wire and could be just as dangerous.
One solution to providing an antistatic carpet that is not dangerous has been taught by Brown and Webber in their application for U.S. patent Ser. No. 643,983, filed June 6, 1967 (now abandoned), and owned by the assignee hereof.
Brown et al recognized that it was possible to blend staple synthetic or natural textile fibers with staple electrically conductive fiber (which could be a textile metal fiber) wherein the electrically conductive fiber constitutes less than one per cent by weight of the blend, in order to provide an antistatic textile yarn or textile fabric. This spun blended staple yarn has been used by the carpet industry as the facing yarn. It has been found that as little as 1/3 to 1/6 of one per cent by weight of the conductive fiber is effective to control a static electricity build-up in a carpet when used continuously in adjacent carpet facing yarns and when a conductive latex coating is applied to the baking fabric.
Although the Brown-Webber method provides a good antistatic carpet made from spun blended staple yarns, it is not adaptable to continuous filament carpets. According to the American Carpet Institute, about 80 percent of all carpets sold in the United States are made from continuous filament yarns and only 20 percent are made from spun yarns. There has been an ever-increasing shift from natural fibers for carpets (i.e., wool) to synthetic filaments which can be made in a continuous form. The Brown-Webber method, although a fine system, is limited to staple carpet facing yarns and therefore not useful in the standard continuous filament carpet field.